Preservação das zonas ripárias e qualidade das águas: estudo de caso da bacia do rio Piranga - MG.

Abstract

The preservation and recovery of riparian zones has been one of the management options most used to mitigate the effects of diffuse pollution on water quality. However, despite the benefits of riparian ecosystems, there are contradictions regarding the effectiveness of these systems in promoting the improvement of water quality in hydrographic basins with different levels of anthropization. In this context, this work seeks to explore the associations between different levels of forest cover in riparian zones (scenario corresponding to the current coverage situation and recovery scenario with all the reforestation of all riparian zones) and water quality, through hydrological modelling (MGB) and water quality (Warm-GIS), at the UPGRH of the Piranga River, in Minas Gerais. The definition of the areas considered as riparian zones followed the provisions of the law and the water quality parameters analysed were: Biochemical oxygen demand, dissolved oxygen, thermotolerant coliforms, Nitrate, Nitrite, and total ammoniacal nitrogen. Only the rainy season was considered, between the years 2005 and 2014, using Q10, discharge with 10% of permanence as the reference flow, since in rain events it is more evident the pollutant carriage in the form of diffuse pollution. Additionally, to the modelling methodology presented, landscape metrics were used in order to characterize this scenario, compared to the current scenario, in terms of landscape distribution, analysing the area, shape, fragment dispersion and species diversity. The results indicated significant improvements in water quality for the variables total phosphorus, nitrate and ammoniacal nitrogen, with percentages of attendance above 10% in relation to the current scenario. The improvements observed were not able to reach the standards established for class 2 water, established by DN COPAM No. 01/2008. Although the presence of riparian forests is associated with improvements in water quality, as observed by the results of the landscape metrics, that indicate improvements in connectivity and diversity, other factors, such as the composition and structure of the region's vegetation, have an important influence on this process. Changes in the local scale of riparian zones have limited impacts, and in order to achieve the objectives proposed by the framing of water bodies, the integrated management of the hydrographic basin in its entirety is essential.